Radomes function to protect antennas such as radar and other antennas and associated equipment from environmental exposure and thus must exhibit suitable structural integrity, be capable of surviving thermal and other stresses, and, in the case of aircraft radomes, be aerodynamic in design. Radomes must also be constructed to achieve certain desired electrical performance characteristics. Electrical considerations include minimum transmission loss, minimum reflected power, minimum beam deflection, and minimum pattern distortion. Typically, there is a trade-off in the design of a radome as between structural/environmental and electrical considerations.
There are many different materials used in constructing radomes and many different cross sectional configurations including single layer (typically made of a composite material), A-sandwich, B-sandwich, C-sandwich, and multiple-layer sandwich constructions. See Rudge, A. W., K. Miene, A. D. Oliver, and P. Knight, The Handbook of Antenna Design, Vol. 2, Chapter 14, Peter Peregrenus Ltd., London, UK and Skolnik, M. I., Introduction to Radar Systems, Chapter 7, McGraw-Hill, New York, N.Y., both incorporated herein by this reference.
In a typical C-sandwich radome structure, there are two honeycomb or other low density core layers separated by a central skin layer and also a skin layer on the outside of each core forming the interior and exterior of the radome.
For electrical reasons, the equivalent lumped circuit susceptance of the central skin layer typically is made to be about twice the susceptance of the outside and inside skin layers. The susceptance of each skin layers is a function of the dielectric constant of the material of the skin layer, its thickness, and the frequency of interest.
In the known prior art, the same material was used for all three skin layers and thus they each had the same dielectric constant. In order for the radome to function electrically by maintaining transparency over a range of frequencies and incident angles, the central skin layer typically has twice the susceptance of the inner and outer skin layers. When all the skin layers are made of the same material, the central skin layer is typically twice as thick as the inner and outer skin layers.
In many radome applications, such as an airborne applications, weight is a critical factor and thus those skilled in the art have long sought various weight reduction techniques while still maintaining the desired electrical characteristics and also maintaining the desired structural integrity of the radome structure.